Background: Immunization or vaccination is the process of inducing artificial immunity against an antigen taking advantage of the mechanisms of immunological memory. Current vaccines include substances known as adjuvants, which tend to improve the immunogenicity of the antigen, reduce the antigen quantity employed, and boost the immune response in weak responders. Unfortunately, only a few vaccine adjuvants are approved for human use. Objective: Thus, the objective of this study was to investigate the effect of Tannic acid on humoral and cell-mediated immunity against bovine serum albumin (BSA) as a protein antigen in Wistar rats. Method: In order to establish the Tannic acid concentration to test it as an adjuvant, the lethal dose 50 and maximum non-toxic dose were calculated through cytotoxicity and hemolytic assays with J774 A.1 cell line and rat erythrocytes by resazurin reduction method and UV/vis spectrophotometry. Thirty Wistar rats were divided into 5 groups that included two controls without antigen and three treatment groups of adjuvants plus BSA as a protein antigen. The rats were immunized in a 30-day scheme. Blood samples were collected for humoral immunity analysis by means of immunoglobulin quantification, isotyping and antigen-antibody precipitation inhibition analysis. Rat peritoneal macrophages and splenocytes were isolated for cell-mediated immunity analysis by means of nitric oxide quantification from adjuvant stimulated peritoneal macrophages and lymphocytes proliferation assay. Results: Tannic acid was capable of increasing the immunogenicity of the antigen; besides, it was able to stimulate cell-mediated immunity by means of increased lymphocyte proliferation. Moreover, Tannic acid improved the humoral response by means of increased specific antibodies titers. These activities may be attributed to pattern recognition receptors stimulation. Conclusion: Tannic acid was considered biocompatible when tested in vivo because the concentration tested did not show cytotoxicity or hemolytic effect, and there was no detrimental effect observed on the animals’ health. These results show Tannic acid as a promising candidate for vaccine adjuvant.

Background: An antigen is a small foreign substance, such a microorganism structural-protein, that may trigger an immune response once inside the body. Antigens are preferentially used rather than a complete attenuated microorganism to develop safe vaccines. Unfortunately, not all antigens are able of inducing an immune response. Thus, new adjuvants seeking to enhance the antigen’s ability to stimulate immunity must be developed. Therefore,the objective of this work was to evaluate the molecular-structure adjuvant activity of tannic acid (TA) coupled to a protein antigen in Balb/c mice. Method: Bovine serum albumin (BSA) was used as an antigen. The coupling of BSA and TA was mediated by carbodiimide crosslinking, and verified by SDS-PAGE. Forty-two Balb/c mice were divided into seven groups including two controls without antigen, an antigen control, an adjuvant control, and two treatment groups. An additional group was used for macrophages isolation. A 30-day scheme was used to immunize the mice. The analysis of humoral immunity included immunoglobulin quantification, isotyping and antigen-antibody precipitation. The analysis of cell-mediated immunity included the quantification of nitric oxide from peritoneal macrophages and splenocytes’ proliferation assay, after treatment stimulation. Results: No differences were found in the antibodies’ concentration or isotypes induced with the conjugate or the pure BSA. However, an immunogenicity improvement (p<0.05) was observed through the specific anti-BSA antibody titles in mice immunized with the conjugate. Besides, macrophage activation (p<0.05) was detected when stimulated with the treatments containing TA. Conclusion: Tannic acid exhibited macrophages’ activation properties. Moreover, when TA is incorporated into the structure of a protein antigen such as BSA, an antibody specificity enhancement is observed. This as a consequence of antigen processing by activated antigen-presenting cells. These results showed the use of tannic acid as a novel candidate for vaccine molecular-structure adjuvant.

Background: The COVID-19 pandemic had infected more than 3.5M people around the world and more than 250K people died in 187 countries by May 2020. The causal agent of this disease is a coronavirus whose onset of symptoms to death range from 6 to 41 days with a median of 14 days. This period is dependent on several factors such as the presence of comorbidities, age and the efficiency of the innate or adaptive immune responses. The effectors mechanisms of both types of immune responses depend on the pathogen involved. In the case of a viral infection, the innate immune response may approach the harmful virus through pattern recognition receptors inducing an antiviral state. On the other hand, the adaptive immune response activates antibody production to neutralize or eliminate the virus. Phenolics are plant secondary metabolites with many biological activities for plants and humans against infection. Chemical modification of proteins may enhance their biological properties; thus, a protein of medical interest, for instance, a viral protein can be used as scaffold to build a biopharmaceutical conjugated or complexated with phenolics exhibiting structural complexity or biological activities to achieve effective phenolic-protein-based therapeutics like vaccine adjuvant complexes, immunogen conjugates, and antiviral conjugates. Conclusion: Pharmaceutical biotechnology applies the principles of biotechnology to develop biopharmaceuticals for protein-based therapeutics; such as adjuvants, recombinant proteins, monoclonal antibodies, and antivirals. As neither a vaccine nor a treatment for COVID-19 is currently available, this manuscript focuses on insights from pharmaceutical biotechnology into phenolic biopharmaceuticals against COVID-19.